OCR Text |
Show Variable Stars. Thoro aro certain stars which show moro or leas conspicuous variations of brlght-1 brlght-1 ness. Among tho six thousand easily vls-. vls-. ible to the naked eyo thero aro between fifty and a hundred of whch this is true; J about half a dozen of thom wcro known before 1S00. If wo includo -tho telescopic stars, the number of known variables Is at present at least thlrteon hundred, and this without taking account of several hundred moro which havei been detected In certain star-cluslorH within tho past five or six yean. Ten years ugo Dr. Chandler s catalogue of variables included only about throo hundred objects. The roll is now Increasing with extrcmo rapidity, rapid-ity, between two and throo hundred having hav-ing been added within the past twelve months. This swift growth Is duo largely to tho utilisation of photography which' through tho comparison of photographs of given portions of the heavens taken at different times, continually brings out new variables. When thus detected" tho nHtron-omera nHtron-omera proctcuVJ.o. study thom In dotall with photometers attached to their telescopes, enabling them accurately to compare the brightness of each Huspccted object from tlmo to tlmo with that of Its neighboring stars, and thus to determine tho amount and character of its variations ns repro-Hented repro-Hented by Its so-called "light-curvo." Jof,-. Charlea A. Ydunt, in Harper's 'Weekly. - - " |